The effect of the distance between wood and coal particles on the characteristics of their joint ignition under conditions of high-temperature radiation-convective heating

Abstract

The article presents the results of the experimental studies of the ignition processes of mixed fuels “wood + coal” under conditions corresponding to the furnace spaces of the boiler units of TPPs. It has been established that under conditions of relatively low ambient temperatures, the time characteristics of the ignition process of coal and wood particles in the composition of the mixture differ significantly from the analogous characteristics for the ignition of single particles. It is shown that woody biomass significantly accelerates the ignition of coal, compared to the ignition of homogeneous coal (the delay time is reduced by 20–30%). At the same time, it has been found that coal particles significantly slows down the process of wood ignition (on average by 30%).The analysis of the distance between particles (d) has shown that d has a significant effect on the ignition performance. It was found that there is a certain “optimal” value of d, at which the ignition delay times are minimal. It is also shown that with an increase in the ambient temperature, the effect of the distance between particles decreases significantly.Based on the results of the experimental studies, a mathematical model has been developed for the ignition of wood-coal fuel particles, which differs from the known ones by a detailed description of thermophysical and thermochemical processes occurring in the porous structure of fuels and in a small vicinity of these particles. A comparative analysis of theoretical and experimental values of ignition delay times has shown their good agreement. An asymptotic analysis of the ignition time has shown that the entire induction period can be conditionally divided into two stages: fuel heating and direct thermochemical reaction. The fuel heating time takes about 90% of the entire induction period.